leto
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| posted on 20/6/06 at 04:10 PM |
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datz510
Nice work there  But i can't help notice that the dampers are in the spot where you might expect to find that wonderful piece of machinery
from Woodward. I fear that moving the rack so far back might cause some unwanted ackerman effects.
Syd Bridge
As most open wheeled race cars take all those drawbacks there must be some advantages too.
“I'm gonna ride around in style
I'm gonna drive everybody wild
'Cause I'll have the only one there is a round”. (J. Cash)
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datz510
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| posted on 20/6/06 at 04:12 PM |
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leto.. it is going to be tight.. that is for sure. I'll cross that bridge when I get there.
One real advantage of a pushrod suspension is the ability to adjust the ride height of the car without touching the shocks. I'll be able to
set damper rebound, spring preload, and ride height independently.
[Edited on 20/6/06 by datz510]
Hang on, we're goin for a ride!
1972 Datsun 510 (1600) w/ 200hp 3.0L V6
1995 Nissan Pathfinder rock crawler
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datz510
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| posted on 20/6/06 at 04:51 PM |
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One other thing I wanted to post.. I'll be picking up one of the 2003-2004 R6 shocks tonight. Because of the parallel nitrogen canister, if
needed, these will allow me to rotate the lower mount to put the shock eyes parallel to eachother.
Hang on, we're goin for a ride!
1972 Datsun 510 (1600) w/ 200hp 3.0L V6
1995 Nissan Pathfinder rock crawler
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leto
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| posted on 20/6/06 at 05:54 PM |
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If I got this right, moving the rack back will make the inner wheel turn faster and the outer wheel turn slower. When you transfer wight towards the
outer wheel, accelerating, braking or turning sharper, the car will under steer. And when you transfer weight back towards the inner wheel, going out
of a corner, the car will over steer. Moving the rack forward will have the opposite, and to my ears more desirable, effects.
I have no idea how significant this effect will be or if it can be compensated. So I might be howling “Wolf” here. 
 
Ackerman effect
“I'm gonna ride around in style
I'm gonna drive everybody wild
'Cause I'll have the only one there is a round”. (J. Cash)
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datz510
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| posted on 20/6/06 at 06:11 PM |
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Yes, moving the rack back helps generate ackerman angle:
http://www.stockcarproducts.com/steer12a.htm
quote:
Fig. 3 - The front end has now been improved by altering the spindles so that their steering arms are permanently diverged with the wheels
still pointed straight ahead. This will generate positive steering toe (Ackerman) while eliminating the necessity for static toe-out. A further
improvement has been made while they were at it: the rack has been moved an inch rearward, which not only helps generate Ackerman but, as a bonus,
straightens the push-pull alignment of the tie rods as the steering angle increases. Compared with Figures 1 and 2, this is going to feel like a whole
new ball game. Not only will corner entry be more positive, but it will now be easier to control the car in a slide.
I'm going to need a little extra ackerman angle, as I've flipped the knuckle arms upside down and rewelded them to convert form a
rear-steer knuckle to a front steer. On measuring it, it still doesnt have enough ackerman though. Currently, my arms intersect at about the center
of the rear axle. Theoretically, they should intersect at about 2/3 the distance between the front and the rear axle, as an intersection at the rear
axle centerline technically is not correct, as commonly thought.
[Edited on 20/6/06 by datz510]
Hang on, we're goin for a ride!
1972 Datsun 510 (1600) w/ 200hp 3.0L V6
1995 Nissan Pathfinder rock crawler
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Syd Bridge
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| posted on 20/6/06 at 06:15 PM |
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quote:
, it's to prevent the paint on the shocker getting chipped .
Yairh, and that's about all it achieves in a Locost or 7 type car. 
Mr Leto, if you can, work out the HP it takes to drag a pair of coilovers through the air at 150mph, then 200mph. Then you'll know why they put
them in out of the airflow, and use nice thin pushrods instead. Also helps with unsprung weight, and polar moments.
If you work out the cost of your time making up all that gubbins, even if you got the coilovers for free, it's still a big expense in time and
materials for no appreciable gain.
Cheers,
Syd.
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datz510
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| posted on 20/6/06 at 06:31 PM |
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The gain is that I have something in the end that both works and is unique. I dont WANT a car like everyone elses. If my chassis gains a few pounds
doing this, so what?
Building unique personalized vehicles is what I like to do. If I put a dollar value on the time I've spent building things, I could have been a
millionaire long ago.
I find it funny that someone can say to another that they shouldnt think outside the box and explore something new, and instead should just can it all
and do it the "accepted" way.
Mabye I get a lot of joy out of solving problems? and spending time tinkering in the garage playing with metal? It is relaxing for me to dive in and
try to figure out these problems. In the end, I'll have a unique and fun car to putter around in, at which time I'll probably sell it to
build something else... and the cycle goes on.
To each his own... This is my car.
[Edited on 20/6/06 by datz510]
Hang on, we're goin for a ride!
1972 Datsun 510 (1600) w/ 200hp 3.0L V6
1995 Nissan Pathfinder rock crawler
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wildchild
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| posted on 22/6/06 at 11:43 AM |
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yeah, if we cant do things our own way, what's the point in building your own car.
incidentally I was looking at a shiny new cossie powered caterham on a dealer stand at a show, and they have gone to pushrods on that model at
least.
i've been toying with doing either push or pullrod suspension for mine. why? well it keeps the shocks clean, looks neater, potentially allows a
wider choice of shocks, is more adjustable, and mostly because I feel like doing something different!
http://www.wildchild.org.uk
Build photos on Flickr
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Syd Bridge
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| posted on 22/6/06 at 04:48 PM |
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STill bemused and amused. Puddin' heads, the lot of ya. If you must you must.
As for Caterham, how much extra do they charge? Plenty of bling and sales hype 'added value'. Not much else.
Cheers,
Syd.
[Edited on 22/6/06 by Syd Bridge]
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JB
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| posted on 23/6/06 at 06:17 AM |
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Inboard Shocks
Pros and Cons of inboard shocks.
PRO
You can get a 1:1 motion ratio. This is good for damping and makes spring swops dead easy.
It keeps your expensive dampers out of the road dirt and wet.
Structurally you can keep all the forces quite central on the chassis without having to cantilever out mountings for the shocks.
It gives a clean front end.
CONS
Extra complication and weight, brackets rockers etc.
The rocker pivot bolt sees double the load compared to the other bolts in the system.
Anti roll bar mounting can be awkward.
It takes up a lot of room in the car.
I have inboard suspension on my car and the biggest attraction to me is the 1:1 motion ratio. However in future if I could get a 1:1 motion ratio with
outboard suspension I would probably go that route.
John
[Edited on 23/6/06 by JB]
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leto
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| posted on 24/6/06 at 06:02 PM |
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The big benefit of a pushrod suspension is not reduced drag, it is the possibilities in suspension tuning and setup. If you know what you are doing,
keeping the dampers out of the dirt is a great way to make a locost faster.
“I'm gonna ride around in style
I'm gonna drive everybody wild
'Cause I'll have the only one there is a round”. (J. Cash)
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Mark18
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| posted on 24/6/06 at 08:42 PM |
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The biggest attraction of inboard suspension for me is that you get rising rate suspension, which curiously noone has mentioned?
Mark
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gazza285
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| posted on 24/6/06 at 11:41 PM |
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Standard suspension is rising rate as well, but for the amount of travel used, its not really important.
DO NOT PUT ON KNOB OR BOLLOCKS!
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crbrlfrost
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| posted on 25/6/06 at 05:44 AM |
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I have to say this is a rather crazy argument to get into. Actually, the localized aero advantages of replacing a spring over damper with a push/pull
rod is pretty good, but when factoring in the rest of the package is does rather dwindle. The reasons regarding suspension tuneability are quite good
and true, as long as the time has been put in to optimize the package within reason. There actually are no unsprung weight advantages, an negligable
if any moment of inertia advantages. There could be slight CofG perks, but again usually minimal. Actually, the overall mass of the system, if roll
bars are to be used, should come out pretty equivilant since the roll bars can be made considerably shorter and thus lighter to make up for the added
weight of the rockers and rods. Ultimately though, I have to say I agree that it comes down to building whatever gets your panties in a twist.
Cheers
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JB
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| posted on 25/6/06 at 05:45 AM |
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Rising and falling Rate Suspension
I do not like changing rate for the following reasons:
I like a balanced, neutral handling car, this means it does what I want without excessive under or over steer. One way of altering the under over
steer balance is to adjust the relative front and rear roll rates. A well set up car will be sensitve to this, for example on my car moving the anti
roll bar drop link 20mm along the bar will change my car from undrivable under steer to un drivable over steer.
Now a rising or falling spring rate suspension changes the roll resistence. If the change at each end is the same then this is not a problem. However
the chances of this happening is very unlikely. So a changing rate suspension just adds another extra complication in this already very complicated
and compromised business.
I can understand why people want rising rate and the dead easy way to do this is to use progressive bump rubbers on the coil overs. These will only
come into play over the biggest bumps.
John
[Edited on 25/6/06 by JB]
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Mark18
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| posted on 25/6/06 at 09:17 PM |
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Are you sure standard is not falling rate? The way I see it, as the damper compresses the angle between it and the lower wishbone becomes more acute,
ie. falling rate?
As has been said it's probably not a huge deal on a locost but you can't deny the advantages of rising over falling rates.
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gazza285
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| posted on 26/6/06 at 05:53 AM |
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quote:
Originally posted by Mark18
Are you sure standard is not falling rate? The way I see it, as the damper compresses the angle between it and the lower wishbone becomes more acute,
ie. falling rate?
? The angle gets nearer 90 degrees as the shocker compresses, hence rising rate.
DO NOT PUT ON KNOB OR BOLLOCKS!
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Syd Bridge
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| posted on 26/6/06 at 08:31 AM |
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quote:
Originally posted by crbrlfrost
I have to say this is a rather crazy argument to get into. Actually, the localized aero advantages of replacing a spring over damper with a push/pull
rod is pretty good, but when factoring in the rest of the package is does rather dwindle. The reasons regarding suspension tuneability are quite good
and true, as long as the time has been put in to optimize the package within reason. There actually are no unsprung weight advantages, an negligable
if any moment of inertia advantages. There could be slight CofG perks, but again usually minimal. Actually, the overall mass of the system, if roll
bars are to be used, should come out pretty equivilant since the roll bars can be made considerably shorter and thus lighter to make up for the added
weight of the rockers and rods. Ultimately though, I have to say I agree that it comes down to building whatever gets your panties in a twist.
Cheers
Prof. Frost,
Care to go over those statements above and revise them? When applied to a Locost you are nearly correct. Applied to an open wheeler,
...........well, you are a good bit wide of the realities.
Cheers,
Syd.
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Mark18
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| posted on 26/6/06 at 01:36 PM |
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quote:
Originally posted by gazza285
? The angle gets nearer 90 degrees as the shocker compresses, hence rising rate.
Just took a look at the car and you're right, I always thought they had falling rate suspension for some reason. This little discovery has just
made my day
Mark
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crbrlfrost
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| posted on 26/6/06 at 08:22 PM |
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Actually Sid, I don't care to revise any of them. My observations are accurate on aero, ie very local improvement with very little overall gain.
On unstrung weight I am right again, inboard suspension often adds to unsprung weight, in both locosts and open wheelers. I said that would be small
but mostly neglible gains in moment of inertia (most of the time they will still lie along the front axle line, sometimes just behind it, but
considering the weight of the dampers in comparison to other components, its a relatively small change), and possible but not likely improvements in
CofG (some people use pull rod and mount the dampers low, but usually it is rocker arm or pushrod with them mounted high. Overall weight of the system
will probably even out if the often heavy rollbars are shortened and connected inboard. If no rollbars, you'll usually end up slightly heavier.
Tuneability is the primary reason to include rockers of any kind, either inboard (most every formula car and many sports racer) or outboard such as
the cantilevered Stohr DSR cars. Formula cars are significantly better positioned to take advantage of the aero gains so that is another good reason
for their inboards. Seems my ultimate conclusion was to do what they liked as its their car. And taking a strong look back at my reasoning, it is
accurate. Cheers.
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Syd Bridge
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| posted on 27/6/06 at 07:58 AM |
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You keep believing that stuff and my work will be secure for a long time.
Cheers,
Syd.
[Edited on 27/6/06 by Syd Bridge]
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wildchild
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| posted on 27/6/06 at 12:16 PM |
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Syd,
If you have such a dislike of pushrod suspension, then why do you keep posting in this thread.
Alternatively, if you are interested in the topic but believe you can provide some proper justification as to why you wouldn't use it, then
we're all waiting to hear it.
I know from other threads that you have a lot of experience and knowledge which you seem fairly willing to share, but then I keep coming back here and
seeing yet another smug dismissive comment. What's the point?
http://www.wildchild.org.uk
Build photos on Flickr
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Syd Bridge
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| posted on 27/6/06 at 03:22 PM |
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I don't dislike it, quite the opposite in fact, just see it as unnecessary in a 7 type car. It goes against everything a se7en is meant to be.
Cheers,
Syd.
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crbrlfrost
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| posted on 27/6/06 at 04:13 PM |
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whatever sid. I've worked the numbers several times myself, and if you don't want to supply reasoning, then I guess there's no point
in posting. Cheers
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Syd Bridge
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| posted on 27/6/06 at 04:30 PM |
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quote:
Originally posted by crbrlfrost
On unstrung weight I am right again, inboard suspension often adds to unsprung weight, in both locosts and open wheelers.
OK Mr.Frost, maybe you might elaborate on that statement. Just how does inboard ADD to unsprung weight. ?????
As far as I am aware, a pushrod is much lighter than a coilover assembly. Have I been mistaken all these years????
When you sort that one out, you may wish to revise the rest. This stuff is my 'bread and butter'. Has been for 20years and more. And
I'm big enough to show that I earn a very good living.
Cheers,
Syd.
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